1 files changed, 46 insertions, 14 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index d90138683a..ca434f0cd2 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1550,21 +1550,37 @@ relock:
 	 * So here we disable page faults in the iov_iter and then retry if we
 	 * got -EFAULT, faulting in the pages before the retry.
 	 */
+again:
 	from->nofault = true;
 	dio = btrfs_dio_write(iocb, from, written);
 	from->nofault = false;
 
-	/*
-	 * iomap_dio_complete() will call btrfs_sync_file() if we have a dsync
-	 * iocb, and that needs to lock the inode. So unlock it before calling
-	 * iomap_dio_complete() to avoid a deadlock.
-	 */
-	btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
-
-	if (IS_ERR_OR_NULL(dio))
+	if (IS_ERR_OR_NULL(dio)) {
 		ret = PTR_ERR_OR_ZERO(dio);
-	else
+	} else {
+		struct btrfs_file_private stack_private = { 0 };
+		struct btrfs_file_private *private;
+		const bool have_private = (file->private_data != NULL);
+
+		if (!have_private)
+			file->private_data = &stack_private;
+
+		/*
+		 * If we have a synchoronous write, we must make sure the fsync
+		 * triggered by the iomap_dio_complete() call below doesn't
+		 * deadlock on the inode lock - we are already holding it and we
+		 * can't call it after unlocking because we may need to complete
+		 * partial writes due to the input buffer (or parts of it) not
+		 * being already faulted in.
+		 */
+		private = file->private_data;
+		private->fsync_skip_inode_lock = true;
 		ret = iomap_dio_complete(dio);
+		private->fsync_skip_inode_lock = false;
+
+		if (!have_private)
+			file->private_data = NULL;
+	}
 
 	/* No increment (+=) because iomap returns a cumulative value. */
 	if (ret > 0)
@@ -1591,10 +1607,12 @@ relock:
 		} else {
 			fault_in_iov_iter_readable(from, left);
 			prev_left = left;
-			goto relock;
+			goto again;
 		}
 	}
 
+	btrfs_inode_unlock(BTRFS_I(inode), ilock_flags);
+
 	/*
 	 * If 'ret' is -ENOTBLK or we have not written all data, then it means
 	 * we must fallback to buffered IO.
@@ -1793,6 +1811,7 @@ static inline bool skip_inode_logging(const struct btrfs_log_ctx *ctx)
  */
 int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 {
+	struct btrfs_file_private *private = file->private_data;
 	struct dentry *dentry = file_dentry(file);
 	struct inode *inode = d_inode(dentry);
 	struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
@@ -1802,6 +1821,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	int ret = 0, err;
 	u64 len;
 	bool full_sync;
+	const bool skip_ilock = (private ? private->fsync_skip_inode_lock : false);
 
 	trace_btrfs_sync_file(file, datasync);
 
@@ -1829,7 +1849,10 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	if (ret)
 		goto out;
 
-	btrfs_inode_lock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
+	if (skip_ilock)
+		down_write(&BTRFS_I(inode)->i_mmap_lock);
+	else
+		btrfs_inode_lock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
 
 	atomic_inc(&root->log_batch);
 
@@ -1853,7 +1876,10 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	 */
 	ret = start_ordered_ops(inode, start, end);
 	if (ret) {
-		btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
+		if (skip_ilock)
+			up_write(&BTRFS_I(inode)->i_mmap_lock);
+		else
+			btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
 		goto out;
 	}
 
@@ -1982,7 +2008,10 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	 * file again, but that will end up using the synchronization
 	 * inside btrfs_sync_log to keep things safe.
 	 */
-	btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
+	if (skip_ilock)
+		up_write(&BTRFS_I(inode)->i_mmap_lock);
+	else
+		btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
 
 	if (ret == BTRFS_NO_LOG_SYNC) {
 		ret = btrfs_end_transaction(trans);
@@ -2051,7 +2080,10 @@ out:
 
 out_release_extents:
 	btrfs_release_log_ctx_extents(&ctx);
-	btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
+	if (skip_ilock)
+		up_write(&BTRFS_I(inode)->i_mmap_lock);
+	else
+		btrfs_inode_unlock(BTRFS_I(inode), BTRFS_ILOCK_MMAP);
 	goto out;
 }